One of Eric Idle's characters briefly compares American beer to making love in a canoe.
While singing the "Sit on My Face" song, the men wear long aprons. At the end of the song, they walk off stage, revealing that they are not wearing anything under the aprons, and their rear ends are visible. Done for comedic effect.
The opening song, "Sit on My Face" is about the 69 sexual position, however the lyrics are so discreet that children are unlikely to understand the sexual undertones.
A woman asks a man if he wants a "blowjob". There is no further emphasis on this reference.
Male characters strip down to reveal female bondage-style gear under their clothes. No real nudity though.